Follistatin 315 vs Follistatin 344
Side-by-side comparison of key properties, dosing, and research.
Anabolic & IGF
Follistatin 315Anabolic & IGF
Follistatin 344- Summary
- Follistatin 315 is a splice variant isoform of follistatin produced by alternative mRNA processing. Unlike Follistatin 344 which is tethered to cell surfaces via heparan sulfate proteoglycans, FST-315 circulates freely in the bloodstream and has broader systemic distribution. It is the predominant circulating form and exerts systemic myostatin inhibition as well as FSH suppression, making it relevant to both muscle growth and reproductive endocrinology.
- Follistatin 344 is a recombinant form of the endogenous follistatin protein. It inhibits myostatin and activin — the primary negative regulators of muscle growth — potentially removing the genetic ceiling on muscle development. It is one of the most theoretically powerful anabolic compounds but is experimental with limited human data.
- Half-Life
- ~3–5 hours (longer systemic circulation vs FST-344)
- ~24–36 hours
- Admin Route
- SubQ, IM
- SubQ, IM
- Research
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- Typical Dose
- No established human dosing protocol
- 100 mcg
- Frequency
- Research use only
- Once daily
- Key Benefits
- Systemic myostatin inhibition for whole-body muscle growth
- Freely circulating — broader tissue distribution than FST-344
- Strong FSH-suppressive activity useful in certain hormonal protocols
- Potential for greater anabolic effect across multiple muscle groups simultaneously
- May be more relevant to reproductive endocrinology applications
- Studied in gene therapy approaches for muscular dystrophy
- Inhibits myostatin — removes muscle growth ceiling
- Significant increases in muscle mass and strength
- Reduces fat mass
- Promotes bone density
- May stimulate hair follicle cycling
- Anti-fibrotic effects in muscle tissue
- Synergistic with IGF-1 and other anabolic peptides
- Side Effects
- Systemic FSH suppression — significant concern for fertility
- Greater potential for off-target effects vs FST-344 due to systemic distribution
- Limited human safety data
- Potential cardiac hypertrophy with prolonged high-dose exposure
- Muscle soreness (from rapid hypertrophy)
- Potential reproductive effects (activin inhibition)
- Unknown long-term safety profile
- Possible esophageal effects at high doses (animal data)
- Stacks With
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